1. Technical Field
The present invention relates to a method of manufacturing an ink for forming a functional layer which is used when a functional layer having a luminescence function is formed and a method of manufacturing an organic EL element.
2. Related Art
An organic electro-luminescence (EL) element as a luminescence element has a functional layer including a luminescence material consisting of an organic compound between an anode and a cathode. As a method of forming such a functional layer, a vapor phase process such as a vacuum deposition method (also referred to as a dry process) and a liquid phase process using a solution in which a functional layer forming material is dissolved or dispersed in a solvent (also referred to as a wet process or a coating process) are known. Generally, a low molecular material is suitably used in the vapor phase process and a high molecular material is used in the liquid phase process from the viewpoint of film forming properties. It is known that the high molecular material is inferior in terms of the luminescent efficiency and the luminescent lifetime in some cases, compared to the low molecular material. On the other hand, since the organic EL element can relatively easily be formed on a large substrate, compared to the vapor phase process, the liquid phase process has been continuously developed.
For example, in JP-A-2006-190759, an organic EL element having a hole injection and transport layer in which a film is formed using a high molecular material by a wet process and a low molecular luminescence layer which is laminated on a hole injection and transport layer and in which a film is formed using a low molecular luminescence material by a wet process is disclosed. As a low molecular luminescence material, an organic compound having an anthracene skeleton or a pyrene skeleton is indicated.
In addition, for example, in JP-A-2008-226686, as a method of manufacturing an organic EL element, a hole injection transport layer is formed by dissolving a triphenylamine-based polymer which is a high molecular material in cyclohexylbenzene as a main solvent and xylene as an auxiliary solvent and then subjecting the resultant to application and drying. In addition, a method of forming a luminescence layer by dissolving a mixture in which a luminescence material which is a low molecular material is doped in a polyolefin-based material which is a high molecular material in a solvent including cyclohexylbenzene and xylene in the same way and then subjecting the resultant to application and drying on a hole injection transport layer is indicated.
Furthermore, for example, in JP-A-2009-245657, as a method of forming a hole injection layer and a hole transport layer, a method of forming a film from a mixed solution of a low molecular layer forming material and a high molecular binder is indicated.
In JP-A-2006-190759, JP-A-2008-226686, and JP-A-2009-245657 described above, in a case where any of the hole injection layer, the hole transport layer, or the luminescence layer consisting of an organic compound among the functional layers having a luminescence function is formed by a liquid phase process, the following organic solvents are indicated as a solvent for dissolving an organic compound of a low molecular material or a high molecular material, or an organic compound which is a mixture of the low molecular material and the high molecular material.
For example, an alcohol-based solvent such as methanol or ethanol, a halogen-based hydrocarbon-based solvent such as dichloromethane or dichloroethane, an aromatic-based solvent such as benzene or toluene, a paraffin-based solvent such as hexane or octane, an ester-based solvent such as ethyl acetate or butyl acetate, an amide-based solvent such as N,N-dimethylformamide or N,N-dimethylacetamide, a ketone-based solvent such as acetone or methyl ethyl ketone, an amine-based solvent such as pyridine or quinoline, a nitrile-based solvent such as acetonitrile or valeronitrile, a sulfur-based solvent such as thiophene or carbon disulfide, and the like are included.
However, depending on a material which is used, the solubility of the low molecular material or the high molecular material with respect to the organic solvent described above is not necessarily big. In particular, in a case where a mixture of the low molecular material and the high molecular material is used, there was a problem in that the low molecular material and the high molecular material may be agglutinated and easily gelled by mutual intermolecular force in the organic solvent, and thus a considerable time (for example, 24 hours or longer) is required until a gel-like mixture to be completely dissolved in the organic solvent, or a gel-like mixture may not be dissolved completely.